The present invention relates to a device for applying a release agent (for instance, silicone oil) to the fixing roll of a plain paper copying (PPC) machine.
The basic process of fixing in a PPC copying machine consists of pressure fusing a transferred toner image to sheet of paper as it is passed between a heated fixing roll and a resilient pressure roll such as a rubber roll. When the paper with a toner image is passed between the heated fixing roll and the resilient pressure roll, several problems occur, such as the paper sticking to the periphery of the fixing roll so as to prevent complete toner fixing, toner particles coming off the copy paper and being deposited on the fixing roll thereby producing a double image (this phenomenon usually being referred to as "offsetting"), and malfunction of the copying machine. While various methods have been proposed for solving these problems, they all depend on the application of a release agent that provides the fixing roll and elastic roll with good release properties.
However, a great deal of difficulty is involved in applying the release agent to the roll uniformly and in the right amount. If the release agent is applied in excessive amounts, it either stains or discolors the paper, and at the same time, rapid consumption of the release agent requires its frequent refilling. Furthermore, the excess release agent solidifies on the roll surface and may cause unexpected troubles. If the amount of application of the release agent is insufficient, offsetting or deteriorated release properties of the roll surface will occur that induces the sticking of the paper to the periphery of the roll. Typical release agents are heat-resistant oils such as silicone oil.
Various types of release agent applicators have so far been proposed, but none of them are completely satisfactory. The applicant previously developed a release agent applicator that permits uniform application of the release agent, consumes a minimum amount of the agent, requires a very small installation area, and which is simple in shape and can be manufactured at a very low cost.
As shown in FIGS. 1A, 1B and 2, this applicator is used with a fixing device composed of a fixing roll 14 and a pressure roll 15 between which copy paper 16 having a toner image 19 is passed so as to pressure fuse the image to the paper. The applicator consists of a porous receptacle in the form of a porous tube 7 of poly(ethylene tetrafluoride) resin which is heat sealed or stoppered at both ends and placed in contact with the fixing roll 14 in its axial direction so as to enable the application of the release agent 6 from the porous tube of poly(ethylene tetrafluoride) resin.
Being soft, the porous tube 7 is carried on a support 1 (FIGS. 1A and 1B) or 4 (FIG. 2) in such a manner that part of the tube projects from the opening of the support. The pores in the area of the porous tube other than the outlet for the release agent are closed with fluorine rubber or any other suitable by, for example, coating or covering techniques, so as to produce a pore closed area. This is done in order to discharge the release agent in a metered and uniform amount.
In FIGS. 1A and 1B, reference numeral 2 indicates the closed-pore area of the porous tube of poly(ethylene tetrafluoride) resin, 3 refers to the pore open area of that tube, and 5 denotes an inlet for the release agent.
The formation of the closed-pore area in the tube may be realized by contact with the support as shown in FIG. 3. The inventors also developed an applicator replacing the porous tube of poly(ethylene tetrafluoride) resin with a porous receptacle in the form of a sheet of the same material as shown in FIG. 4. However, even these prior art applicators are not completely defect free. During the copying operation, the projecting part of the porous sheet or tube is dragged by the rotating fixing roll, deforming to such an extent that complete application of the release agent is prevented.